The present invention relates to acoustical modeling of sound sources. Preferred embodiments may be coupled to the ear canal. In particular some embodiments relate to a wearable device configured to be modeled as both a part of the source and a part of the load in an electro-acoustical source-and-load model of a system where a sound source is coupled to the ear canal. Such a wearable device may be used to determine the acoustic energy density at a point of measurement in or near the ear of a user. An earpiece according to an embodiment according to the present invention comprises a tube and acoustic sensors.